Catshark egg capsules from a Late Eocene deep!watermethane!seep deposit in western Washington State, USA

STEFFEN KIEL, JÖRN PECKMANN, and KLAUS SIMON

Kiel, S., Peckmann, J., and Simon, K. 2013. Catshark egg capsules from a Late Eocene deep!water methane!seep depositin western Washington State, USA. Acta Palaeontologica Polonica 58 (1): 77–84.

Fossil catshark egg capsules, Scyliorhinotheca goederti gen. et sp. nov., are reported from a Late Eocene deep!watermethane!seep calcareous deposit in western Washington State, USA. The capsules are preserved three!dimensionally andsome show mineralized remnants of the ribbed capsule wall consisting of small globular crystals that are embedded in amicrosparitic matrix. The globules are calcitic, but a strontium content of 2400–3000 ppm suggests that they were origi!nally aragonitic. The carbonate enclosing the egg capsules, and the capsule wall itself, show !13C values as low as!36.5‰, suggesting that formation was induced by the anaerobic oxidation of methane and hence in an anoxic environ!ment. We put forward the following scenario for the mineralization of the capsule wall: (i) the collagenous capsules expe!rienced a sudden change from oxic to anoxic conditions favouring an increase of alkalinity; (ii) this led to the precipitationof aragonitic globules within the collagenous capsule wall; (iii) subsequently the remaining capsule wall was mineralizedby calcite or aragonite; (iv) finally the aragonitic parts of the wall recrystallized to calcite. The unusual globular habit ofthe early carbonate precipitates apparently represents a taphonomic feature, resulting from mineralization mediated by anorganic matrix. Taphonomic processes, however, are at best contributed to an increase of alkalinity, which was mostlydriven by methane oxidation at the ancient seep site.

Key words: Elasmobranchia, Scyliorhinidae, taphonomy, exceptional preservation, collagen, Late Eocene, Washing!ton State, USA.

Steffen Kiel [skiel@uni!goettingen.de], Georg!August Universität Göttingen, Geowissenschaftliches Zentrum, AbteilungGeobiologie and Courant Research Center Geobiology, Goldschmidtstr. 3, 37077 Göttingen, Germany;Jörn Peckmann [joern.peckmann@univie.ac.at], Universität Wien, Erdwissenschaftliches Zentrum, Department fürGeodynamik und Sedimentologie, Althanstr. 14, 1090 Wien, Austria;Klaus Simon [ksimon@gwdg.de], Georg!August Universität Göttingen, Geowissenschaftliches Zentrum, AbteilungGeochemie, Goldschmidtstr. 1, 37077 Göttingen, Germany.

Received 13 July 2011, accepted 7 November 2011, available online 8 November 2011.

Copyright © 2013 S. Kiel et al. This is an open!access article distributed under the terms of the Creative Commons Attri!bution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original au!thor and source are credited.

IntroductionMethane seeps in the deep sea are sites on the seafloor wheremethane!rich fluids are expelled. Such sites are often colo!nized by lush faunal communities dominated by animals liv!ing in symbiosis with chemotrophic bacteria, which take ad!vantage of the abundance of methane and hydrogen sulfide atthese sites. This high biomass on the otherwise nutrient!poordeep!sea floor attracts various fishes that appear to have theability to cope with the elevated levels of hydrogen sulfide atthese sites. The most common fishes at methane seeps arezoarcids, macrourids, and occasionally hagfish, eels, morids,and a few other groups (Ohta and Laubier 1987; Hashimotoet al. 1989; MacAvoy et al. 2002; Turnipseed et al. 2004;Sellanes et al. 2008). Reports of sharks from modern meth!ane seeps are restricted, to the best of our knowledge, to thetwo species Centroscyllium granulatum (Dalatiidae) and

Halaelurus canescens (Scyliorhinidae) at seep sites in740–870 m water depth northwest of Concepción Bay, Chile(Sellanes et al. 2008). In situ observations and stable isotopeand fatty acid studies indicate that most of these fishes feed,at last to some extent, on chemosymbiotic animals, althoughthis is unclear in case of the sharks (MacAvoy et al. 2002,2003; Sellanes et al. 2008).

Living catsharks often attach their egg capsules to erectstructures in the water column, such as gorgonians, octocorals,hydroids, and even derelict fishing gear (Able and Flescher1991; Etnoyer and Warrenchuk 2007). Recently, catshark eggcapsules were found associated with worm tubes and carbon!ates at a deep!water methane seep site in the eastern Mediter!ranean where the worm tube thickets might provide a substratefor protection and ventilation (Treude et al. 2011). At a LateEocene methane!seep deposit in western Washington, USA,large numbers of similar egg capsules were found associated

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with worm tubes, as well as hexactinellid sponges (Treude etal. 2011), showing that catsharks have been using such envi!ronments as nurseries for at least 35 million years. Predatorshave a significant role in ecosystem functioning and maintain!ing diversity. By serving as nurseries for predatory deep!ma!rine catsharks and other elasmobranch taxa, methane seeps areimportant components of deep!sea ecosystems and should notbe considered as only extreme and exceptional habitats; theirpresence or absence is likely to influence faunal diversityalong continental slopes (Treude et al. 2011: 179).

Elasmobranch egg capsules are rare in the fossil record.Perhaps most common among them are the Paleozoic and Me!sozoic spirally coiled capsules of the Palaeoxyris group foundmainly in freshwater deposits (Fischer and Kogan 2008).There are occasional occurrences of chimaeroid egg capsules(Chimaerotheca) ranging back to the Triassic (Brown 1946;Bock 1949). Skate egg capsules are rare, with a few specimensfrom the Oligocene of central Europe, named Rajitheca (Stei!ninger 1966). All these records represent internal or externalmolds, many are flattened, and a capsule wall has, to the bestof our knowledge, never been reported. The scope of the pres!ent contribution is to (i) name the fossil egg capsules found inthe Bear River methane!seep deposit, (ii) provide a detaileddescription of the capsule and its mineralized wall, and (iii)discuss the fossilization process.

Institutional abbreviations.—GMUG, Geowissenschaftli!ches Museum der Universität Göttingen, Germany; SMF,Senckenberg Museum, Frankfurt, Germany; USNM, UnitedStates National Museum of Natural History, WashingtonDC, USA; UWBM, University of Washington, Burke Mu!seum, Seattle, USA.

Other abbreviations.—EDX, energy!dispersive X!ray spec!troscopy; LA!ICPMS, laser ablation!inductively coupledplasma mass spectroscopy.

Geological settingThe Bear River limestone is an isolated carbonate bodyfound within uplifted deep!water siltstone beds mapped as“Siltstone of Cliff Point” (Wells 1989). It has long been inter!preted as an ancient seep deposit based on its geological set!ting and the macrofaunal association (Goedert and Squires1990; Goedert and Benham 2003; Kiel 2010a). The low !13Cvalues of the carbonate reported here provide unequivocalevidence for its origin at a methane!seep site. The host sedi!ments were deposited in the Cascadia accretionary wedgeduring the Eocene when subduction of the Juan de Fuca plateunder the North American continent started, and their exhu!mation started in the Miocene (Brandon and Vance 1992;Stewart and Brandon 2004). Foraminiferal associations indi!cate that the Bear River seep deposit formed in water depthsof 500–2000 m (Goedert and Squires 1990; Kiel 2010b). Themacrofaunal association is dominated by the mussel Bathy!modiolus willapaensis, worm tubes are common, large sole!

myid, lucinid, and vesicomyid bivalves occur throughout thedeposit, as well as numerous small gastropods (Goedert andSquires 1990; Squires and Goedert 1991; Squires 1995;Goedert and Benham 2003; Kiel 2006, 2010a). A peculiarfeature of this seep deposit is the abundance of uncrushedspecimens of the hexactinellid sponge Aphrocallistes poly!tretos (Rigby and Jenkins 1983) that are intermingled withmussels, worm tubes, and the egg capsules reported here.

Material and methodsThin sections of 60 µm thickness were prepared from crosssections of a specimen with the ribbed capsule wall pre!served. They were studied using a Zeiss Axioplan opticalstereomicroscope (lamb: Visitron HBO 50; filter: BP 365,FT 395, LP 397), and a Zeiss 510 Meta confocal laser scan!ning microscope (LSM). The LSM was run with an excita!tion of 488 nm, emissions in the range of 490–704 nm weremeasured with spectral detection using a Lambda detector.

Samples for scanning electron microscope (SEM) imag!ing and EDX analysis were mechanically removed from thecapsule wall, etched for ca. 10 seconds in 10% acetic acid,mounted on an aluminium sample holder, and coated with14 nm of platinum. Images were taken with a LEO 1530SEM at 3.8 KV, EDX analysis were done with an attachedINCAx!act analyzer at 15.7 KV.

Samples for stable carbon and oxygen isotope analysiswere extracted from the polished surfaces of the same rocksamples from which thin sections were prepared, using ahand!held microdrill. Samples from outside the capsule wallwere drilled from in between and up to a few millimeters awayfrom the ribs; those from inside the capsule were drilled onlyfrom the micrite, not from any of the microsparitic or cementphases. Carbonate powders were reacted with 100% phospho!ric acid at 75"C using a Kiel III online carbonate preparationline connected to a ThermoFinnigan 252 mass spectrometer.All values are reported in per mil relative to V!PDB by assign!ing a !13C value of +1.95‰ and a !18O value of !2.20‰ toNBS19. Reproducibility was checked by replicate analysis oflaboratory standards and is better than ±0.05‰.

The mineralogy of the capsule wall was investigated byRaman spectroscopy. Spectra were recorded using a HoribaJobin Yvon LabRam!HR 800 UV micro!Raman spectrome!ter with a focal length of 800 mm. As excitation wavelengththe 488 nm line of an Argon Ion Laser (Melles Griot IMA106020B0S) with a laser power of 20 mW was used. The la!ser beam was dispersed by a 600 l/mm grating on a CCD de!tector with 1024"256 pixels, yielding a spectral dispersion of0.43 cm!1. An Olympus BX41 microscope equipped with anOlympus MPlane 100" objective with a numerical apertureof 0.9 focused the laser light onto the sample. With these set!tings, the focal point of the laser on the sample had a diameterof ca. 1 µm. The confocal hole diameter was set to 100 µm.The acquisition time was 15 seconds for wave numbers in therange of 100–2000 cm!1. For calibration of the spectrometer

78 ACTA PALAEONTOLOGICA POLONICA 58 (1), 2013

a silicon standard with a major peak at 520.4 cm!1 was used.All spectra were recorded and processed using LabSpecTM

version 5.19.17 (Jobin!Yvon, Villeneuve d’Ascq, France).Trace element analysis of the capsule wall was done by la!

ser ablation!inductively coupled plasma mass spectroscopy(LA!ICPMS), using a PerkinElmer SCIEX ELAN DCR IImass spectrometer coupled to a Lambda Physik Compex 110Argon!Fluoride!laser with a wavelength of 193 nm. Sampleswere placed in a low!volume sample chamber with a size of5"3"0.5 cm (L"W"H) that was flushed with argon gas. Eachspot was measured for 10 seconds with a spot size of 10 µm.

Systematic palentologyThe terminology follows Ebert et al. (2006).

Genus Scyliorhinotheca nov.Type species: Scyliorhinotheca goederti gen. et sp. nov. described be!low.Etymology: From Scyliorhinidae, the catshark family that presumablyproduced those egg capsules; and from Latin theca, envelope, capsule.

Diagnosis.—Egg capsules generally having the elongated,

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KIEL ET AL.—EOCENE CATSHARK EGG CAPSULES IN METHANE!SEEP DEPOSIT 79

A B

C

D

E

F

G

10 mm

10 mm

10 mm

10 mm

10 mm10 mm

10 mm

Fig. 1. The Late Eocene Bear River egg capsule Scyliorhinotheca goederti gen. et sp. nov. in different states of preservation. A. Steinkern showing the anteriorand posterior ends (USNM 544321). B. Posterior half of a steinkern, showing the tapering end with a horn (USNM 544322). C. Deformed steinkern with spin!dle!like shape (USNM 544323). D. Steinkern with faint wrinkles on the surface, perhaps due to shrinkage (USNM 544324). E. Two specimens: the lower,main specimen shows the anterior constriction and the flattened anterior end (left) and remnants of the ribbed capsule wall (right); the upper specimen (arrow) isjust a cast of a ribbed capsule surface; note relics of worm tubes on the right side of the block (USNM 544325) (image from Treude et al. 2011). F. Steinkernshowing indentation on lower left (USNM 544326). G. Cast (external mold) showing ribbing on capsule surface (USNM 544327).

inflated fusiform shape of those of living catsharks (Scyli!orhinidae), with or without longitudinal ribs.

Scyliorhinotheca goederti gen. et sp. nov.Figs. 1–3.

Etymology: For James L. Goedert, who discovered these fossils.Holotype: Almost complete internal mold USNM 544321 (Fig. 1A).Paratypes: Internal and external molds; all figured specimens are de!posited in the USNM (numbers 544322 to 544328); additional speci!mens are deposited at SMF (P9796 to P9798), UWBM (95285 to 95287)and at GMUG (GZG.IF.11020).Type locality: The Bear River seep deposit, southwestern WashingtonState, USA (46"19.943 N, 123"55.964 W). This is LACM locality num!ber 5802 and UWBM locality number C1459.Type horizon: Siltstone of Cliff Point, latest Eocene (nannofossil zoneCP15b of Okada and Bukry 1980), based on the presence of Isthmo!lithus recurvus).

Diagnosis.—The egg capsules have an inflated fusiformshape and a slightly constricted waist; the maximum dimen!sions are: length = 50 mm, width = 15 mm, thickness = 11mm. The surface shows at least 12 rough ridges and two thinsecondary ridges. The lateral edges extend to narrow lateralflanges along the entire length of the egg case. The anteriorborder is slightly concave, with two well!developed respira!tory fissures but apparently no horns; the posterior end is ta!pering after a slight constriction, and the horns are short andpointing at, or twisting around, each other.

Discussion.—We have seen no tendrils on either end of theegg capsules, but this may be a preservational artefact. Themost similar egg capsules produced by modern catsharks arethose of the scylorhinid genus Apristurus: many have a simi!larly tapering posterior end, and some show coarse ribs on thesurface (Sato et al. 1999; Iglésias et al. 2002, 2004; Flammanget al. 2007). Fossil teeth attributed to the genus Apristurus areknown from the Late Eocene of European Tethys (Adnet et al.2008), which agrees with the stratigraphic age of the egg cap!sules reported here. The only other extant scylorhinid with afossil record ranging into the Eocene, including the PacificNorthwest of the United States, is Scyliorhinus (Welton 1972;Adnet et al. 2008); although the egg capsules of this genus re!semble those of Apristurus in general shape (Rusaouën et al.1976; Ebert et al. 2006), they are apparently smooth (cf.Treude et al. 2011). Similar in outline are the egg capsules oftwo species of the genus Schroederichthys (S. tenuis and S.maculatus), but on their surfaces the egg capsules show onlytortuous longitudinal striations (Springer 1966; Gomes and deCarvalho 1995) instead of strong ribs as in the Bear Riverspecimens.

The capsule wallIn cross section, the capsule wall is approximately 100 µmthick; individual ribs are up to 700 µm high and between 100and 150 µm wide at their narrowest point; they are often bentsideways (Fig. 3A, B). The capsule wall consists of a micro!

sparitic matrix enclosing abundant and roughly evenly distrib!uted globules having a diameter of 15–20 µm (Fig. 3C, D).The matrix and the globules are both made of calcite, indicatedby peaks at the Raman bands at 280, 710, and 1084 m!1 (Fig. 4;Urmos et al. 1991). The tips of the ribs are often made ofsparry calcite (Fig. 3C, D). Under crossed nicols, the matrixshows extinction in patches, some of the globules also showextinction, some do not (Fig. 3F). Confocal laser scanning mi!croscopy shows that the globules have a much stronger auto!fluorescence than the matrix (Fig. 3E). LA!ICPMS analysis ofthe globules (N = 3) showed a Sr content of 2400–3000 ppm,measurements on the background matrix (N = 2) showed a Srcontent of 1300–2700 ppm. The small size of the globules andtheir close proximity to each other within the wall matrixmeant that LA!ICPMS measurements of the globules werecompromised by certain amounts of wall matrix material, andvice versa (Fig. 5). It is thus likely that the actual Sr contents ofboth globules and wall matrix are more distinct from eachother than we were able to document. Small pyrite framboids

80 ACTA PALAEONTOLOGICA POLONICA 58 (1), 2013

5 mm

10 mm

Fig. 2. Silicon rubber casts of external molds of the Late Eocene Bear Riveregg capsule Scyliorhinotheca goederti gen. et sp. nov. A. USNM 544327(the same specimen as in Fig. 1). B. USNM 544328.

Table 1. Stable carbon and oxygen isotope values of the capsule wall andthe carbonate associated with it; all values are relative to V!PDB.

!13C !18O

Outside capsule !35.1 !6.6

!35.2 !6.0

!36.3 !5.8

Capsule wall !36.0 !4.4

!36.5 !6.3

Inside capsule !34.9 !5.0

!35.1 !5.0

!35.1 !4.9

no larger than 5 µm diameter (most are < 1 µm diameter) aredispersed throughout the wall matrix (Fig. 6), as revealed bySEM imaging and EDX analysis of etched surfaces of the cap!sule wall. The Raman spectra (Fig. 4) of the wall matrix showa small peak at 375 m!1, which also indicates pyrite (Mernaghand Trudu 1993). This peak was not seen in the spectra of theglobules (Fig. 4).

Preservation and occurrence

All specimens are preserved in three dimensions, and severalshow indentations that most likely originated after hatching ofthe young shark (Fig. 1F). Many capsules are only preservedas internal molds (steinkerns; Fig. 1), some are external molds

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KIEL ET AL.—EOCENE CATSHARK EGG CAPSULES IN METHANE!SEEP DEPOSIT 81

A B

C D

E F

500 µm 500 µm

200 µm 200 µm

50 µm50 µm

Fig. 3. Thin section micrographs of the capsule wall of the Late Eocene Bear River egg capsule Scyliorhinotheca goederti goederti gen. et sp. nov.A, B. Two sections of a capsule wall with several ribs, dark, micritic seep carbonate on the outside, and several diagenetic carbonate phases in the interior;plane!polarized light. C, D. Close!up on the middle rib in A, rotated ca. 90" clockwise. Note that the capsule wall consists of microsparite, enclosing globu!lar calcite crystals; plane!polarized light (C) and UV light (D). E. Detail of the capsule wall; laser scanning microscope image generated by linear unmixingusing the spectra of the globules versus that of the wall matrix. F. Detail of capsule wall, showing extinction of some of the globules; crossed!polarized light.

showing the ribbing of the capsule wall (Figs. 1, 2), and onlyin a few specimens is the capsules wall preserved in the miner!alized form described herein. The egg capsules are enclosedin, and filled with, micritic, microsparitic, and peloidal car!bonate as well as carbonate cement that show !13C values aslow as !36.3‰, the wall itself revealed values of !36.5 and!36.0‰ (Table 1). The capsules are always associated withworm tubes (Fig. 1E) and three dimensionally preserved spec!imens of the hexactinellid sponge Aphrocallistes polytretos,and often also with the mussel Bathymodiolus willapaensis(cf. Squires and Goedert 1991; Kiel 2006).

DiscussionShark egg capsules are virtually unknown from the marinefossil record (Fischer and Kogan 2008). Freshly laid catsharkegg capsules are made of collagen (Rusaouën et al. 1976),a substance that is quickly hydrolyzed when exposed to water.Thus, the calcification of the capsule walls requires specialconditions. We suggest the following scenario for the genesisof the calcitic capsule wall: (i) the egg capsules experienced asudden change from an oxic to an anoxic environment; (ii)aragonitic globules precipitated within the collagenous cap!sule wall, likely favoured by the activity of bacteria degradingthe organic wall; (iii) subsequently the remaining wall matrix

was mineralized by aragonite or calcite; (iv) finally the ara!gonitic parts of the wall recrystallized to calcite. This scenariois based on the following lines of evidence:

Environment.—When catshark egg capsules at modernmethane!seep sites are laid into tubeworm thickets they de!velop in a fully oxic environment (Treude et al. 2011). At theBear River site, the very low !13C values of the capsule walland the carbonate surrounding it, as well as the finely dis!persed pyrite framboids show that at least part of the carbon!ate formed due to the anaerobic oxidation of methane (cf.Peckmann and Thiel 2004) and thus in an anoxic environ!ment. Because collagen is quickly hydrolyzed in marine en!vironments, we assume that a sudden change from an oxic toan anoxic environment facilitated the three dimensional pres!ervation of the egg capsules and their walls.

Shape and mineralogy of the globules.—The growth of cal!cium carbonate globules like those documented here is com!monly related to bacterial activity and the bacterial decay of or!ganic matter (e.g., Buczynski and Chafetz 1991; Briggs andKear 1993), but crystal habit is clearly not an unequivocal cri!terion for this kind of mineralization (e.g., Fernández!Díaz etal. 1996). The low !

13C values of the capsule wall includingglobules suggest that wall fossilization (i.e., replacement ofcollagen by carbonate minerals) was fostered by an increase ofalkalinity induced by anaerobic oxidation of methane (cf.Peckmann and Thiel 2004). Although the globular crystalhabit—a habit untypical for methane!derived carbonate miner!als of seep limestone—most likely reflects the taphonomicalalteration of the organic wall, the decay of the wall was appar!ently not responsible for the generation of an oversaturationwith respect to carbonate minerals. Even so carbonate precipi!tation was probably mediated by an organic matrix provided bythe decomposing wall, the decay of the collagenous wall didnot contribute significantly to alkalinity increase based on thevery similar carbon isotopic compositions of the wall and theadjacent methane!derived carbonate phases; shark collagentypically reveals higher !

13C values of approximately !15‰ to

82 ACTA PALAEONTOLOGICA POLONICA 58 (1), 2013

Globule

Wall matrix

Re

lativ

ein

ten

sity

Re

lativ

ein

ten

sity

Raman shift (cm )-1

1084

280

710

375

250 500 750 1000 1250 1500 1750 2000

Fig. 4. Raman spectra of globules and microsparitic matrix of the capsule wall.

outside

capsule wall

inside

Fig. 5. Thin section micrograph of the capsules wall showing three of thecraters produced during laser ablation (arrows).

!13‰ (MacNeil et al. 2005). An originally aragonitic mineral!ogy of the globules is suggested by their high Sr content(2400–3000 ppm); such values are common for aragonite, butcalcite or dolomite precipitated in marine environments typi!cally have lower Sr contents (Tucker and Wright 1990; Comp!ton 1992). Aragonite cement formed at methane seeps in theBlack Sea exhibits Sr contents as high as 9500 ppm, the associ!ated high!Mg!calcite revealed values of approximately 1200ppm (Peckmann et al. 2001). Similarly, aragonite cement ofseep carbonates from the Niger Delta showed Sr contents of upto 12 000 ppm, much higher than the contents of 100 ppm to1000 ppm found for other carbonate mineralogies includingcalcite and dolomite (Bayon et al. 2007). Savard et al. (1996)reported as much as 11 000 ppm Sr in aragonite cement of Cre!taceous seep limestone rocks. In many ancient seep deposits,aragonite is recrystallized to calcite (Buggisch and Krumm2005; Peckmann et al. 2007). Fibrous calcite cements with aninferred aragonite precursor of Paleozoic seep limestone rocksrevealed Sr contents as high as approximately 20 000 ppm(Iberg deposit; Buggisch and Krumm 2005), 13 000 ppm(Tentes Mound; Buggisch and Krumm 2005), and 13 000 ppm(Dzieduszyckia deposit; Peckmann et al. 2007), whereas themicrite (i.e., microcrystalline calcite) of ancient seep depositstypically exhibits contents in the range of a few hundred ppm tolittle more than 1000 ppm (e.g., Campbell et al. 2002).

Wall matrix.—Mineralization of the wall matrix subsequentto the precipitation of the globules is suggested by the regularshape of the globules. The growth of such globules within analready existing calcium carbonate wall seems impossible.Based on the Sr content of the wall matrix, ranging from1300–2700 ppm, it is difficult to decide whether this carbon!ate was primarily aragonite or a mixture of aragonite and cal!cite. The very negative !13C values of the capsule wall (glob!ules plus matrix) and the pyrite framboids finely dispersedthroughout the wall indicate that fossilization occurred underanoxic conditions. The Bear River capsule walls share acommon fossilization mechanism with the tubes of seep!dwelling vestimentiferan worms (Haas et al. 2009) in that

fossilization was driven by carbonate precipitation inducedby the anaerobic oxidation of methane. Unlike the fossiliza!tion of the organic!walled tubes of vestimentiferans, how!ever, where individual layers of the organic wall function astemplates for carbonate cement growth, the egg capsulewalls were permineralized by authigenic carbonate, resultingin three!dimensional preservation.

ConclusionsTo the best of our knowledge, the catshark egg capsules re!ported here are the first fossil shark egg capsules from a fullymarine environment. The shape of the fossil egg capsulesclosely resembles that of egg capsules produced by moderncatsharks (family Scyliorhinidae), therefore we erect the newgenus and species, Scyliorhinotheca goederti. Fossilization ofthe capsule wall was favoured by anaerobic oxidation of meth!ane—the biogeochemical key process at seeps—inducing re!placement of the organic wall by carbonate minerals. Thecrystal habit of the first replacive carbonate phase, however,reflects taphonomical processes within the decaying wall.

AcknowledgementsWe thank Jim Goedert (Wauna, Washington State, USA) for providingthe specimens and for discussion, Gernot Arp for help with the confocallaser microscope, Axel Hackmann for preparation of thin sections,Nadine Schäfer for her time and effort with Raman spectroscopy,Gerhard Hundertmark for photography, Dorothea Hause!Reitner forassistance with SEM imaging and EDX analysis (all University ofGöttingen, Germany), Michael Joachimski (University of Erlangen,Germany) for stable isotope analysis, Jan Fischer (Bergakademie Frei!berg, Germany) for discussion of, and literature on, fossil elasmobranchegg capsules, as well as Jürgen Kriwet (University of Vienna, Austria)and an anonymous reviewer for their efforts to improve the manuscript.

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